1. Field of Invention
This invention concerns a torque regulating coupling for connecting an impact wrench drive to a wrench socket used to tighten threaded fasteners so that the maximum torque applied to the fastener can be limited to a predetermined value, and more particularly, to a torque regulating coupling featuring a slider, movably mounted within a coupling body which is adapted to be connected to the wrench drive, and a multi-element, torque transmission member axially disposed within the coupling body and arranged to be connected to a wrench socket for engaging the fastener, the slider being movable along the length of the transmission member to regulate the maximum amount of torque delivered from the wrench drive to the fastener.
2. Prior Art
Because of their speed and ease of use, impact wrenches have become extremely popular for tightening and loosing threaded fasteners featured in all types of mechanical systems. In the typical application, the threaded fastener is a nut or bolt assembly used to join mating mechanical components. In use, the impact wrench, which characteristically includes a wrench drive in the form of a gun and a wrench socket to fit the nut or bolt to be tightened or loosened, requires only that the operator affix the appropriately sized socket to the drive, fit the socket over the nut or bolt, and press the trigger.
The gun, most commonly pneumatically powered, then produces a stream of rotary impulses that are transmitted to the socket and fastener to effortlessly turn down or withdraw the nut or bolt. As is well known in the art, impact wrenches feature a drive having a rotary hammer that on application of power periodically strikes an anvil connected to the wrench drive output to produce the stream of rotary impulses that can be subsequently applied to the nut or bolt.
As is well known and as would be appreciated by those skilled in the art, the torque impulse applied by the impact wrench is designed such that while the peak torque may exceed the yield point of the nut or bolt assembly being tightened, the duration of the impulse is made short enough so that in normal operation the elastic limit of the assembly is not reached. Accordingly, though the peak torque might be sufficient to break the nut or bolt assembly being tightened if the peak torque were applied continuously, since the peak torque is applied for a short time i.e., the duration of the impulse, the assembly is not damaged in normal operation. In this regard, further understanding of the design and operation of impact wrenches may be found in, for example, U.S. Pat. No. 3,744,350.
While impact wrenches have proven themselves to be an invaluable aid to mechanics, assembly works and all others required to put together and take apart mechanical systems, problems have arisen with their use. Because impact wrench users when tightening nuts or bolts usually merely either listen to and/or watch the nut or bolt to determine when they are "tight enough", improper and uncertain amounts of torque are commonly inflicted on the assemblies. In tightening nuts and bolts, the impact wrench, by virtue of the applied stream of impulses, rotates the nut or bolt in successively smaller increments as the nut or bolt tightens. This gives rise to a characteristic "hammering sound" and accompanying "rotary blur" that diminishes in pitch and view, respectively, as the nut or bolt is tightened. As a result, for the sake of convenience, most users simply stop when they feel the sound and blur have diminished "enough" to satisfy the particular needs of the assembly they are working on.
But, this estimated "enough" leads to uncertainty at best, and at worst to either damaged or dangerously under-fastened assemblies. If the finally applied torque is too great, fasteners become damaged or sheared and matting parts deformed. Additionally, substantial difficulty can be encountered in attempting to take apart such assemblies. On the other hand, if the finally applied torque is too low, potentially dangerous, inadequately fastened assemblies can result which are susceptible to coming apart on their own.
The problems of improper and inaccurate torque application have been of concern to the impact wrench industry for some time. However, though a number of approaches have been proposed for more accurately fixing the maximum torque applied by an impact wrench, none of the approaches thus far proposed have provided a simple, compact, and inexpensive solution that enables an operator to quickly, easily and cheaply regulate the torque finally applied.
For example, though Raff, in U.S. Pat. No. 3,744,350, proposes a variety of devices, each featuring a drive receiving member connected to a wrench member by a fixed, resilient element; for example a rubber bushing, spring, slotted sleeve, etc., for limiting the amount of torque applied to a fastener, none of the proposed devices includes means for adjusting the amount of torque transmitted. Accordingly, though the Raff design is able to establish a maximum applied torque, a user would be required to maintain a substantial inventory of devices for each of the maximum torque values likely to be set. Further, the user would be compelled to undergo the inconvenience of interrupt operation, disconnect the old device and replace it with a new one of different rating each time the maximum applied torque was sought to be changed.
On the other hand, though adjustable torque limiting devices have been proposed, their designs have been either awkward in form and operation, or expensive to make and use. For example, while Schoeps, in U.S. Pat. No. 3,832,916, describes an adjustable torque limiting device for use with an impact wrench, it requires use of a coupling sleeve from which a coaxial torsion bar must be extracted and maintained. In accord with the Schoeps design, though the maximum transmitted torque can be adjustable set, to do so the torsion bar must be withdrawn from the device sleeve in fixed spans producing a lengthy and awkward structure susceptible of misalignment and associated rotary instability in operation. While Schoeps notes that fixed-length adjustable devices having an internal element movable along a bar had been known prior to his design, he states such device were found to produce large losses in impact energy and accordingly, presumably, were found undesirable.
Still further, Reynolds in U.S. Pat. Nos. 2,822,677 and 3,129,571 discloses yet additional approaches for adjustable, torque-limiting devices. However, the Reynolds' devices, as described in his patents, calls for use of complicated, mechanical assemblies that require a torsion bar to be rotationally pre-stressed using splined and/or geared assemblies in order to adjust the maximum torque transmitted. However, as is apparent from the descriptions given, due to the use of the mechanically sophisticated splined and geared assemblies, the proposed devices are inclined to be difficult and expensive to manufacture, rendering them unsuited for mass markets.